text:
How is the strength of the material needed in an LTA balloon estimated?
What are the main factors that determine how much load is put on the material/how strong it has to be?
On the one hand I read how balloon fabrics even on smallest piloted hot air balloons are advanced rip-stop multi layered high tech stuff that's also not cheap but then on the other some generic PET film turns out strong enough to lift a man with only 25 micron thickness - that's thinner than some trash bags!

How much safety margin do you want?

So, you have some relatively small pressure differential between inside and outside that you have to maintain, so the material needs to be strong enough to withstand that.  Then you have the suspension of the weight distributed to the surface most likely via some netting, so the envelope material needs to be able to withstand those focused point loads.  But then you have other engineering objectives:  Porosity limits.  Durability and service life, including rip-stop.  Field repairability. Weight. Cost. Stowed size.  UV, flame, chemical, sediment resistance. Rain absorption.

In ASTM F2355-14, "structure requirements for ... balloons ... are presented in details."  I haven't bought a copy of that specification myself, but someone who has could quote those details here.


text:
How are weather balloons different from "regular" big latex balloons?
If I search the internet for "weather balloon" I get much higher prices than if I just look for "big balloon". Just to compare these two listings in particular: this \$320 weather balloon claimed to lift 2kg vs this \$5 big balloon which one can calculate to lift 2.5kg+. Which makes me wonder what the drastic difference in quality must be? Is the former supposed to be much 64 times as durable? But aren't weather balloons supposed to pop when they reach a certain height anyway? And the latter seems to withstand a man sitting on top of it, is that really not durable enough to fly up in the sky?

Short answer: because it is expensive making a large balloon capable of high altitude flight.
Balloon lift is displaced air minus weight of balloon so if you want to do high altitude flight you need something light weight, would suspect that particular $5 balloon is going to be heavy, quite possibly using most of that 2000g nominal lift just supporting itself.
Weather balloons are also intended to expand as they go up to partially overcome the decreasing air density with increasing volume. If your need is just to have an oversize balloon to play with on a string the $5 model would be fine floating around at <50 feet, but if you are trying to actually lift a payload any balloon capable of having someone sit on it would level off at a very low altitude.
The price difference comes back to quality and materials. Weather balloons are normally natural latex to get the stretch needed for the volume increase at low enough weight. This is an expensive and fussy material to work with needing careful control of the raw materials (coming from plants) and humidity during processing. For the $5 version they can use some sort of cheap polymer, and going much thicker any minor variations will matter far less. Having a 0.1mm thinner patch on a 2mm thick balloon is rather less of a problem than 0.1mm less on a 0.2mm balloon.
There may also be some degree of cost because people will pay it. If you are flying a couple of thousand dollars worth of payload spending a couple of hundred to get a reliable balloon is easy to justify.
Would also suggest some creative pricing on that a $320 weather balloon, some random googling for actual weather equipment sellers makes it looks like someone is re-selling with a markup.

Also to note: you may have seen on school freezing a normal balloon and then hitting with an hammer. Temperatures at high altitude are not too much warmer than in such experiment, and you do not want that the balloon break so easily (e.g. on change of wind direction). So total different uses, so different engineering constraint (and so price).

"Weather balloons are also intended to expand as they go up" Indeed. They grow to multiple times their sea level diameter near their maximum altitude before the balloon bursts and falls back down.

I've handled a weather balloon that was made of cellophane (or some similar inelastic plastic) it carried a radiosonde.

@jasen, interesting, that sounds similar to the metalised film used for some 1000kg and up payload flights that get a careful partial fill at sea level and then unfold rather than stretch. Not heard of them in weather balloon size, quite possibly worth a separate answer especially if you can find anything online on cost/capability.

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text:
Why do balloons no longer have nets?
In this 1944 documentary it is claimed that a netted balloon would work as a parachute when torn, other sources seem to confirm that. Disadvantages are not mentioned, nor can I think of any. Yet it doesn't seem like one can find a netted LTA balloon anywhere today.
Also no steerable balloon (or airship) seems to have been built with a net at any point in time.
I can only wonder what the deal breaker with nets is?

Balloons have nets! Not only one but several. The nets are just integrated into the envelope.
If you look at this image, you'll see white lines forming a first net.

On a smaller scale, the fabrics used for the envelope are usually ripstop. This type of fabric integrates strong fibers separated by only a few millimeters, making it a second net. The net of fibers effectively stops small tears from spreading across the envelope.

That's not the same as an independent netting system around the envelope. Modern hot air balloons have been known to fail, and they come apart along the panel joints, ripstop or no ripstop.

@JohnK Do you have examples? I've checked the accidents listed on https://en.wikipedia.org/wiki/List_of_ballooning_accidents and have not see a single one where an external net would have made a difference.

I dimly recall reading about panel failures years ago where the ballon descended fast and landed hard, but I couldn't find anything online either, probably because such incidents didn't result in fatalities. You could have panel blowouts just like with parachutes which are made with similar fabrics, especially if the fabric is weakened by age and UV exposure. The other thing is you need the lower half of the envelope to be able to float up into the upper half for it even to work.  I posted an answer that gets into the technical discussion.

rip stop fabric is, simply, not a net.

@Robe that list does not include non-fatal accidents.

Mostly the consideration will be weight penalty vs risk.  Modern envelope materials and construction reduce the risk of a complete envelope failure, such that you would want a separate netting enclosure to perform that parachute rescue function, to a negligible level. This review of balloon accidents seems to show that spontaneous envelope failures are just too rare to be concerned about.
That is, the risk is not sufficient to justify the weight penalty and the handling difficulties of a separate "rescue" netting system (just the bulk of a netting system would require a way bigger trailer to haul around, and its weight would be a lot of grief to handle and move around by a ground crew). It's just too much hassle to bother with for the theoretical protection it provides.
It's similar to parachute rescue systems for light airplanes. Yes they are in use now, but are still really rare in proportion to the fleet, and in any case their existence isn't to cater to structural failures where a plane comes apart spontaneously while flying along minding its own business, but more for flight into IMC situations and such.  Parachute systems for ultralights are common because those machines are structurally less reliable and are closer to the "old" balloon model, where you wanted a backup for an envelope that had a significant risk of coming apart by itself.
On the other hand, if you had a rash of spontaneous hot air balloon envelope failure accidents, the risk analysis would change, and you might see a "parachute effect" recovery netting system get developed, using advanced materials, that would be feasible.
But feasible means things like a netting system that is disconnected from the envelope below its widest point, with a  gas envelope that can be disconnected at the base, where the heat source is, so that it can move up inside the upper half while "parachuting", that is also light (so a much larger envelope itself isn't required) and easy to handle on the ground.
If you think it through from an engineering perspective, you start to run into technical issue after technical issue, and realize this system could start to get pretty complicated and heavy, leading to the classic "more of this requires more of that, which requires more of this, which requires more of that" engineering weight-complexity-cost merry-go-round. and you're back to "Ah, it's not worth it".

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Why have supercritical airfoils not been used in designing the propeller blades?
In terms of specific fuel consumption, propellers are more economic than jet engines at low speeds (<0.5 Mach) but at high speeds, the propeller blade tip reaches locally to supersonic speeds which results in wave drag and loss of efficiency. Since supercritical airfoils are designed primarily to delay the onset of wave drag in the transonic speed range. Why we haven't used supercritical airfoil sections for propeller blade designs?

Do you know for a fact the we haven’t?  There are some pretty advanced propeller designs out there on modern turboprop aircraft, I’m pretty confident that many smart engineers have squeezed every possible bit of inefficiency out of these new designs.


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What are these points in the Propeller Schematic?

If it matters, this is taken from EASA PPL questions.
The graphic appears to be taken from the side point of view, although I've never seen such a round Spinner, unless it's a variable pitch propeller and it's just the ball bearing joint the blade is attached to.
So far my guess is that the points correspond to the following:

Angle of Incidence (confirmed)
Geometric wing twist (not sure)
Angle of Attack (90% sure)
Aerodynamic wing twist (not sure)

C: is Chord line
D: is Direction of air flow  (I think it refers to the Relative Airflow)
R: is Direction of rotation (I guess clockwise in this case)

2,3,4 could be any of the following "Geometric wing twist", "Angle of Attack" and "Aerodynamic wing twist"

Do you have any more context, or is the question simple "label these points"?  Because that would be a really crummy question...

The gray circle is indeed the joint to which the propeller is attached. The spinner is not shown in this figure.

If my below explanation answers your question, please mark it so. Many thanks!

Like in your last question, you are asking us to label a figure which you have taken from the Aircademy Ltd. PPL question catalog.
In this case, the figure is from Part-FCL Question Bank 80 – Aircraft General Knowledge, Question 65:

So the one label you have been able to "confirm" is the one already marked out in the question catalog.
What you are looking for to label the remaining points is a propeller blade section velocity diagram. A simple one is provided in Figure 5-44 of the excellent FAA Control Flying Handbook, FAA-H-8083-5. More advanced ones are provided in scientific publications, such as Figure 7 in "An Overview of Model Tests and Numerical Predictions
for Propeller-Ice Interaction"

Velocity diagram for a propeller blade section, $\beta$ is the angle of advance, $\beta_i$ is the hydrodynamic pitch angle, $\phi$ is the geometric pitch
angle, $\alpha_G$ is the geometric angle of attack, $V$ is the carriage speed, $V_A$ is the advance speed,  and $U_A$ are the tangential and axial induced velocities, and $P$ is the pitch at $0.7R$.

In short:

point
label

1
blade pitch (=angle of incidence)

3
angle of attack (angle between relative wind and chord line)

4 and 2 are velocities which are not mentioned in the main course materials and would not be relevant for the exam.
As a general recommendation, I suggest you purchase the training material (textbooks) by Aircademy Ltd., since you are clearly preparing for your exam using their question catalogs. The expense will be inconsequential compared to the rest of your training cost - but it would enable you to look up these figures without having to resort to StackExchange multiple times.

Thanks, do you know if the learning materials come in English too?

None of these are "twist."
If the length R represents the speed of the propeller, then 2 is the "adjacent" side of a triangle, allowing you to calculate the length of D using the Pythagorean formula.
4 represents the forward airspeed of the aircraft in proportion to R, which allows you to calculate 3, the angle of attack.

"None of these are "twist."
Agreed, but they are now, as this is how the questions were translated.


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Can an aircraft takeoff while another is still exiting the runway?
Today I was at a non towered airport and I just had landed, while I was beginning to turn off the runway, I saw a light sport behind me takeoff, while I was still on the runway. I was just starting my turn when I saw him fly over my back. Is this legal?

Hi Ben, welcome to aviation.stackexchange. Which country are you flying in?

Did the plane leave the ground before reaching your position when he started his roll?


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Is there a standard format to exchange airspace information in electronic form?
I am looking for information about airspace definitions.
On maps they look great and a pilot has no problem reading maps and NOTAMs, but what about autopilots? Do they use some kind of standardized interface/database? If it exists, where is it defined?
I am not specifying a country because hopefully there only one standard (or an extremely limited set). Should this not be true, I would like to focus on Europe and North America.

Why would the autopilot need to know about airspace definitions? Route definitions should be enough or am I missing something? Even without route definitions, an autopilot could work just with the data entered through the mode control panel.

@DeltaLima I was thinking about something along the lines of Garmin, that has an "autopilot" but also displays the airspaces around for when the pilot is in charge

Aeronautical Information Exchange Model

@RonBeyer if you convert that to an answer, I'll accept it, it is what I was looking for!

The Aeronautical Information eXchange Model (AIXM) was designed to provide a standard model of data exchange for things like:

Aerodrome/Heliport including movement areas, services, facilities, etc.
Airspace structures
Organisations and units, including services
Points and Navaids
Procedures
Routes
Flying restrictions

The Forum on the AIXM site is pretty responsive but relatively quiet. The data available through AIXM seems to be mostly European based but the system was not designed to be restricted to EU.

The majority of GPS navigators and FMS have a dataloadable navigation database.  The actual database each uses is typically encrypted and compressed using proprietary algorithms.  The source data for all of these databases normally start out in ARINC 424 format.  Unfortunately, A424 is not available free of charge.

ARINC 424 is an international standard file format for aircraft navigation data maintained by Airlines Electronic Engineering Committee and published by Aeronautical Radio, Inc.. The ARINC 424 specifications are not a database, but a "standard for the preparation and transmission of data for assembly of airborne navigation system data bases".

The databases are compiled by companies such as Jeppesen. Jeppesen collects the data from the controlling agencies around the world, checks it, and merges it into a world-wide database that they then sell (typically via subscription).
Some information for US airspace is available directly from the FAA.  It is not in a format that can be directly loaded onto aircraft, but may be of use offline.

@ymb1 Thanks for the supplemental information.  To avoid any name confusion, it should be noted that Aeronautical Radio, Inc. changed its name to ARINC some time back.  To further muddy the waters, Rockwell Collins bought ARINC a few years back to gain access to their data link services business (the money making side).  To avoid a conflict of interest, RC sold the industry standards portion of ARINC to SAE-ITC where they now operate as ARINC Industry Activities.

There's also a "new" kid on the block: The open source initiative Open Flightmaps offers curated eAIP for many countries free of charge. The custom format OFMX is a fork of AIXM 4.5 which adds and will add new features and modify very few existing features in order to accommodate things like proper obstacle groups, plate packages etc. It should be fairly easy to adapt an existing AIXM 4.5 parser to consume OFMX by following the migration guide.

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Under EASA rules, what do I need to do to be able to perform aerobatics?
In addition to the aerobatics mentioned in the title, I would also be interested into formation flying.
Is there a specific licence to be acquired? Does a licence covers both?
What are the requirements?

The appropriate rules are in FCL.800 Aerobatic Rating

A licensed pilot may not undertake aerobatic flights unless they hold an Aerobatic Rating
40 Hours of Flight Time (or 120 launches for sailplanes as PIC) completed after issue of respective license
Aerobatic Training course including theoretical knowledge and 5 hours or 20 flights
Aerobatics must subsequently be flown in same category aircraft as used for rating
No revalidation/renewal requirements
Be issued a certificate of satisfactory completion of the instruction for the license endorsement

So there is no specific license to be obtained, however there is a specific rating, which is just an endorsement in your logbook.
Its not clear from the documents that I've read that formation flying qualifies as aerobatics. Some other countries don't consider formation flying an aerobatic operation.

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text:
Do pilots make a lot of money?
How much money do commercial pilots make per year, and per hour? Is there significant non-monetary compensation, such as free hotels stays and food?

This is very variable depending on the time a pilot has been in with the company, the company itself, and maybe even the nation the airline is based in.

Depends on how you define "a lot".

This definitely needs to be narrowed down to be a good question. It depends on what country the airline is in, whether the pilots are flying regional or long haul flights and on what type of aircraft, and what type of employer they work for (passenger airline, cargo company, private charters, government), among other things.

I wouldn't really want to fly with a pilot who's only in it for the money.

Commercial pilot pay depends vastly on what type of work he or she is doing.

@fooot Believe me I sympathize with your concerns, but I feel like the question shouldn't be about just one airline or just one country. The most important aspect here is, I think, "if I decided to become a pilot, what kind of income could I expect" or "is the typical pilot wealthy or poor", which a lot of people have. So I am not sure how to narrow it down without making too specific to be interesting.

I can only answer from a US standpoint as that is the jurisdiction I know best, elsewhere in the world things may be different.
The first thing you can check is this data from the Bureau Of Labor And Statistics according to their data

2015 Median Pay
The wage at which half of the workers in the occupation earned more
  than that amount and half earned less. Median wage data are from the
  BLS Occupational Employment Statistics survey. In May 2015, the median
  annual wage for all workers was $36,200.
For Pilots the 2015 median pay was 102,520 USD per year

You should read over this article as well as it covers a wide variety of how pilots are paid and the such.
Here is some more data on salary as well. You should how ever note that for many articles the data is submitted by choice and may not accurately reflect the true pay scale.
Here is some discussion on the per hour pay but I should caution you to be weary of per hour statistics for pilots. In many cases these numbers are computed using flight hours which does not accurately reflect how much a pilot may work as there is more time involved in a flight than just what the hobbs meter records. Here in the US it is my impression most commercial (121) pilots are salaried.
My two flight instructors recently went to the regionals after completing their ATP hours from talking to them it is evident that starting pay is very low (under 30K a year).
One interesting (and often debated issue) is that the FAA requires pilots to retire at 65 (was previously 60). This in theory puts a cap on their earning potential as an airline pilot (however they can fly non 121 operations like a 135 charter afterwords).
As for perks, that depends on the airline (and may to some extent depend on seniority). Its common to get some comped tickets for family members and the such but its not what it once was. I have heard that many pilots can fly standby on their own (or in company) airlines for free. They may also be able to ride in the jump seat if there is one. This can be attractive for a young single pilot but is not very efficient for family travel.
Free hotels and things will depend on the route you are flying. If overnight stay is required they may put the pilot up (i.e. long haul routes) but you should not expect 5 Star Penthouses and bottomless lobster dinners. However there are plenty of short routes for which a pilot may end up back at their base at the end of their shift.
If you are looking for a decent overview of the pilots life I would advise picking up a copy of Cockpit Confidential it has a lot of the answer you may be looking for and is very to the point.

Unless they had extensive military flight experience before turning to flight instruction, I don't think your flight instructors went directly to "the majors" after getting to ATP minimums, especially not directly from flight instructing. From that and the starting pay you mention, I think you are referring to that sector of the airline industry referred to as the "regional airlines".

Yes you are correct, by majors I was implying they stopped flying the charters they were flying (local stuff in a King Air 200 mostly) ill edit to reflect. FWIW they ended up at Air Wisconsin and Piedmont

That's messed up that I make more than a new ATP piloting a truck. I sure hope they move up quickly

@TomMcW It can still be worth it, despite the low pay :) Money is not everything.

Money is not everything, true. But money buys everything...like your own plane...to fly anywhere you choose on your own schedule.  My pilot life warning to young folks: flying professionally is great until you want to own stuff.


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What is the difference between a cold-stream thrust reverser and a conventional one?
What is the difference between a cold-stream thrust reverser and a conventional one? It seems that all engines emit hot air, due to the combustion process.

Turbofan engines don't push all air through the combustion chamber. Instead part of it runs along the sides.

This bypass region is where the (cold) air stream is redirected from to create the reverse thrust.

Keep in mind that the "cold stream" isn't really cold.  According to this article http://www.google.com.lb/patents/US5666802 it is about 100* Celsius (due to the heat of compression), whereas the hot stream is in the 500 - 600 deg. celsius range (due to the heat of combustion).

Not all air that flows through a turbofan engine undergoes combustion. In a turbofan, part of the air (in some engines, most of the air) is bypassed around the power turbine; that air is simply accelerated by the compressor fan and is vented, cold, out the back of the engine to provide thrust.
A cold-stream thrust reverser simply deflects this cold, bypassed air forward, whereas a "normal" thrust reverser deflects the main engine exhaust.
Wikipedia has some pictures and more description.

A "normal" thrust reverser deflects both of course, not just the hot stream.

@JanHudec: Unless, of course, your engine is a turbojet, which has only a hot stream.

Adding images to already existing answers.

Hot flow (primary flow)
These reversers use both air from the combustion in the core (purple) and air from the flow bypassing the core (blue):

(Source)
This design was used early on turbojets, and is still used on turbofans with a limited bypass ratio.

Cold flow (secondary or bypassed flow)
These ones use only the bypassed flow accelerated by the fan (the large rotor at the front of the engine, here in gray):

(Source)
Modern turbofan engines have large bypass ratios, e.g. 80% of air is bypassed. It makes sense to use reversers only on this flow. As the flow bypassing the core doesn't take part in the combustion process, it is known as the "cold flow".
(One door is open, the other is closed, this is for illustration only ; doors are always either all open or all closed).

Hybrid
Some engines had the two types together (perhaps the early Pratt & Whitney engine of the McDonnell Douglas C-17, but I'm not sure):

(Source)
This combination was used to get a powerful reverse thrust.

The nice colorful images have been taken from this site unfortunately only in French: L'avionnaire.


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What does an Air Battle Manager do?
I heard someone talking about a position in the U.S. Air Force called an Air Battle Manager or ABM. What does a person in this position do?

Do we have a military SE?  This really seems like it should be there if there is one...

Wikipedia has a 1,400-word article on this. Did you read it?

Air battle manager has the following duties:

Plan and execute theater air operations
Analyze national defense strategy
Develop and conduct flying and simulation exercises
Conduct, manage, evaluate and improve unit training and readiness
Create operational policies

Further information can be found at AirForce's website.
In USAirForce, there are seven categories of aeronautical ratings. They are:

Pilot
Navigator
Combat Systems Officer (CSO)
Air Battle Manager (ABM)
RPA Pilot
Observer
Flight Surgeon

For further reading about these ratings, read here.

Isn't this the type of thing a typical officer does? Is an Air Battle Manager different from the typical USAF officer in any way?

@flyingfisch I added some more details. Are you asking about difference in responsibilities between ABM and a pilot?

Ah, thanks, those details helped :)


text:
How does a national ATC make money?
I was reading last week of the public listing of the Italian ATC provider.
In the article it is said that

If successful, the IPO would mark the first listing of a European national air traffic controller, although not the first privatisation.

and this got me wondering: how do they make money? Usually private companies are there to make a profit, do airlines have to pay the ATC providers?
It made me wonder also about possible impact on safety and security: I assume that this is in accordance to EASA rules, but is there any specific mention of "private ATC", or is it permitted simply because it is not forbidden?

Unlike the USA, many other countries have hefty fees for aviation, even general aviation which makes it even more expensive to fly. These fees pay for aviation services like ATC.

@RonBeyer That's true, but of course in the US the money still has to come from somewhere and the FAA does get income from fuel and passenger taxes (among other sources). ATC in the US certainly feels 'free' compared to other countries where they actually send you a bill, but operators are still paying; it's just in a different way than in other countries.

@Pondlife Very true, there have been proposed bills in the past to shift some of these fees to GA which luckily have been closed down before getting too far. A good search is "GA User Fees". They've come up a lot more recently since the FAA keeps running out of funding.

In Europe, airlines pay so-called route charges for flying through national airspaces. EUROCONTROL, the European aviation organisation, collects route charges from their Central Route Charges Office, CRCO, and then distributes the money to the member states, who in turn will distribute them to the national air navigation service providers (ANSP's) - including private ones. The advantage of collecting route charges centrally, is that airlines only have to pay to a single organisation, in a single currency.
The charge for individual flights is calculated based on distance flown and aircraft weight, which are multiplied by a unit rate. The unit rates are determined by the individual countries - they are not the same across all of Europe. Unit rates are based on the actual costs for providing air traffic services, such as ATC, communication facilities, navigation equipment, meteorological information, aeronautical information service and so on.
Route charges do not apply to aircraft weighing less than 2 tonnes, state and government flights and search and rescue flights. Some states also exempt military flights, training flights, test flights, local flights, VFR flights, humanitarian flights, police flights etc.
You can read more about the CRCO here, and about how route charges are determined here.
Regarding your second question, I fail to see why a private ANSP should be any less safe than a government one.

NAV CANADA has been private since 1996, though it is run as a non-profit company.


text:
Is special equipment required to perform high-voltage line inspections?
I was watching a youtube video about high voltage cable inspections performed with helicopters. It can be seen how the helicopter has to reach the same electric potential as the wire, something that normally does not occur to other crafts.
I was wondering, is there any kind of special instrumentation/equipment that must be installed on the helicopters to perform such operations?
Are the pilots aided in any special way to maintain a stable hover or it boils down to skill and training?

There seem to be two questions.  Are you asking about electrical effects, or just the hovering bit, or both?

@Simon about instrumentation/equipment, and I can see two elements that could affect it: hovering next to cables, and electricity.

The electrical side isn't a problem.  Once the potentials are equal, there is no current flow (that's what's happening with the sparks jumping the gap when the linesman uses the bonding wire and rod to bring the helicopter to the same potential as the line).  Once they are at the same potential, nothing happens.

I work in this area and, to my knowledge, I never heard about any special aid to help the pilot. They know precisely which are the wind speed limitations to do the work safely, the rest is basically skill.
What they do install in helicopters, is the so called Wire Strike Protection System (WSPS), which should cut the cable if the helicopter strikes it, avoiding damages on the main rotor (see the picture https://upload.wikimedia.org/wikipedia/commons/b/bf/Ntsp-oh58-N170FR-070205-01cr.jpg that Bell has two WSPS, one over the cabin another underneath the avionics bay). But this is more important on power line inspection, which is made at around 60-80 km/h with cameras and LiDARs. When the helicopter is hovering by the cables this doesn't bring much aid.
But this is a risky job anyway and if you search, you will find plenty of accidents which happened with helicopters and power lines.


text:
What are Baro-Aiding and Baro-VNAV systems?
I've tried searching online as to what the architecture of these systems look like, and I can't seem to find any hardware information. And if it's not a hardware but instead a software, which software uses it and how do you know if you have it?
As far as I know, in the DA40 with G1000 that my flight school flies, we do not have either Baro-Aiding or Baro-VNAV. I understand roughly how they work, but I have yet to find an example of a system that has either. Can someone provide examples of systems that do utilize Baro-Aiding or Baro-VNAV?

Many corporate jets use a baro-aided VNAV system.  Before WAAS was so prevalent, many FMS installations were certified to TSO c129 standards allowing the operator to fly RNAV GPS approach procedures to both LNAV and LNAV/VNAV minima.
Universal, Collins and Honeywell all have FMS hardware that use the onboard ADC to calculate a psudo glidepath the FMS can project as a VNAV path on the PFD.
I don't know if Garmin ever had a system that uses baro-aided glidepaths.

As mentioned on previous answers, Baro-VNAV system combines lateral GPS position with barometric altitude.
The approach is retrieved from navigation system database which includes the MAPt position and elevation and required glide slope angle. Combining the two, the system is able to calculate the required altitude respective to the aircraft position.
The deviation between desired altitude and aircraft’s indicated altitude is displayed as deviation in a similar fashion to ILS glide. But because the glide slope is calculated onboard, it is prone to errors such as aircraft position (wrong distance to the MAPt), wrong QNH setting and cold temperatures.
Baro-VNAV is available in any modern transport category aircraft.

They are a combination of software and hardware. The GPS must have access to an altitude encoder or static source to use baro-aiding or baro-VNAV. It also must be equipped with software that can take advantage of the altitude source to provide vertical guidance on an approach.
The capabilities of G1000s varies by aircraft. For example, some G1000-equipped King Airs are capable of baro-VNAV.


text:
Can ATC reject a GA aircraft IFR flight plan to a busy Bravo/Charlie airport?
This may be a dumb question, but can ATC reject or amend your flight plan to prevent a GA training aircraft from flying into a busy airport (i.e. Atlanta)?
As an example, flying VFR near Nashville, they rarely will allow us (GA training aircraft) to practice an approach in or do a touch and go at KBNA. But if we had it filed on an IFR flight plan, is ATC REQUIRED to allow us the approach or do they have the option to reject or amend us to another airport at their own discretion?


text:
Are airliners shielded from cosmic radiation?
Are airliners shielded from cosmic radiation, what materials can blocked this type of radiation?

No.
Airliners aren't radiation-shielded. Even high-altitude spy planes like the U-2 and SR-71 weren't shielded.
The problem with shielding is that it's heavy. The goal is to put as much mass as possible between you and the source of whatever type of radiation you're worried about. But engineers go to great lengths to keep aircraft weight down. 1 cm of lead shielding around a 737 would weigh about 13,000 kg, about 20% of its maximum takeoff weight. This amount of lead would block about 50% of gamma radiation and cosmic ray doses.
Now, is this bad?
For passengers, definitely not. Even frequent flyers don't spend enough time at cruising altitude for the increased dose to matter.
Sea level cosmic ray doses are about 0.06 µSv/hr. At 35,000 it's about 6 µSv/hr. So a person who stays on the ground for a year gets a cumulative annual cosmic ray dose of 0.5 mSv. A frequent flyer who spends 100 hours in the air in a year gets a dose of 1 mSv. A twofold increase may sound like a lot, but a chest CT scan is about 7 mSv, and the normal background radiation dose (including cosmic rays as well as other forms of ionizing radiation) is 2-4 mSv.
For pilots, who spend a lot more time in the air, it matters more. A pilot who flies 1,000 hours in a year gets a cosmic ray dose of about 6.5 mSv, about a chest CT scan's worth. Over a few decades this does in fact add up to an observable, but not dramatic, increase in cancer rates.
Still, this increased risk for aircrew has not (yet) economically or politically outweighed the cost of shielding.

@TypelA Comparing to CT chest is not high, but from your data, radiation is a hundred times bigger at flight than on sea level.

@user0422 that's correct (I've seen estimates ranging from 35 to 100x higher "at altitude" depending on what is being measured, where and how). But don't forget that "100 times more than almost nothing is still almost nothing. The ratio isn't important. The total dose and the effects of that dose are.

@TypeIA - Let's also not forget that most people spend almost all of their time at sea level and maybe a small handful of hours a year in a plane

I read that commercial aviation avoids the magnetic North pole, because of the radiation risk. This isn't cosmic rays, but what comes out of the sun during a solar storm. The magnetic poles are "holes" in the protection afforded elsewhere by the Earth's magnetic field. Of course, there's also the fact that magnetic compasses don't work there.

No, they are not, and this is not a concern for regular passengers (extreme frequent flyers might want to estimate their exposure, though).
For pilots it is a concern, and at least some companies/jurisdictions will have regular checks and possibly compensation for the exposure that is accumulated during service.
Source: I am very close to a recently retired airline pilot and we went over this exact topic.

"possibly compensation for the exposure " Compensate with money? Health must be on first place.

@user0422 some of the compensation measure involve early retirement to prevent over-exceeding exposure limits (kind of equating it to hard labour), compensation is not necessarily monetary in nature in my understanding.

This is potentially a concern for airplane electronics, and even more so for spacecraft electronics. Cosmic rays can flip a bit in RAM or cause other problems, which can result in software crashing or doing something different from design. It really doesn't matter if one passenger a day has their in-flight entertainment system crash. But it does matter if the auto-pilot or the engine controls don't work as expected.
There are a number of things done to harden critical systems. One of the most important is redundant systems are used. This helps minimize (nothing can totally eliminate computer problems - that's why we have humans in the loop) computer problems, whether due to cosmic rays, faulty parts, software bugs, loose wires, electrical surges or any other causes from taking the systems offline. The odds of one flight computer having a problem on a particular flight due to a cosmic ray is very, very low. The odds of multiple flight computers on the same flight having similar problems due to cosmic rays is really, really, really low.
In theory the flight computers could be shielded really well to protect from cosmic rays - much as the flight records ("black boxes") are built to withstand a typical crash - but there are plenty of other reasons why computers can fail, so putting the extra weight into redundant computers instead makes a lot of sense.

In the aerospace world so called radiation hardened electronic components can be used if needed, so this is not really an issue.


text:
Deviation within an airway
I'm a plane spotter with only general information about air traffic. I'm aware that airplanes can fly only alongside airways. They should fly on the middle of the air routes. However, each airway is defined by its width which suggests me that an airplane has some flexibility within the airways.
My suspicion was somehow confirmed when I spotted a regular cruise (at 38,000 ft) which is passing more or less just above my house (in Europe). I noticed that sometimes this airplane passes above my location +/- a few kilometers away (usually < 10 km, which I also checked on FR24). Or maybe they just fly using different parallel airways?
I have the following questions:

Can a pilot decide how to fly within a single airway? If not, can a pilot or airline choose one of close, parallel airway?
Is there a way to get a list of passed airways for a particular flight?

If passengers could ride up front, some of them would freak out b/c of the 1000 ft vertical separation and GPS nav systems that are super precise. When on a published airway, there is no longer any dispersion of airplanes to either side of the airway from tolerance scatter of the nav equipment; everybody is centered EXACTLY. Airplanes going the other way pass precisely 1000 ft above or below, and when their contrails first come into view a couple miles out, they look like they are coming straight at you until they are less than a mile away.

I'm aware that airplanes can fly only alongside airways.

Your information is slightly out of date. There was a time when all IFR planes were required to stay on defined airways, but that has changed. I'm not sure exactly when it changed, and a quick Google search for the info turned up nothing, but it's been several decades at least. The airways do still exist, and are heavily used whenever possible to make traffic planning easier, but there's nothing wrong with flying between points with no airway connecting them.
Of course, VFR traffic has always been free to fly whichever direction they want, as long as they obey visibility regulations, ask permission for controlled airspace, etc.
But to answer your question: When you're on a route, you're supposed to fly as close to the route centerline as possible. However, it may not always be possible to do that, so the routes do have a defined width that you can maneuver in if needed.

Low-altitude VOR routes (V-routes) go between VOR stations. Since VOR navigation gets more imprecise the further you are from the VOR, the width of the airway reflects that. If you're greater than 102nm from the nearest VOR, the width of the airway is based on a calculation of the margin of error for the VOR; the further you are, the wider the airway is. Within 102nm, the width is simply 8nm (i.e 4nm on either side of the centerline)1.

High-altitude VOR routes (J-routes) don't have a defined width. You're simply expected to stay as close to the centerline as possible.

RNAV routes (T-routes for low altitude, Q-routes for high) are always 8nm wide 2.

When I began my career in the 80's a lot of commercial aircraft (probably 50% or so) in the US used some form of RNAV equipment to fly point to point.


text:
Can commercial jet airplanes be designed to prevent a human from being ingested into the engines?
We've heard terrible news stories of humans occasionally being accidentally ingested into commercial jet engines. It is possible to design the engines in a way that would prevent that from ever happening, like with some type of cage screen in front of the engines, or would that be impossible since it would disturb the air flow to the engines too much?

Ito prevent this inflight, sure, just put all the seats behind the front of the engine intakes... But all design decisions have associated costs as well as benefits...

Mounting the engines really high, like this would reduce the risk, but wouldn't eliminate it entirely, and it would generate its own set of problems, i.e. with engine maintenance. Procedural safeguards make these sorts of accidents rare, but sadly, not impossible.

Would a cage screen in front of a jet engine even do a good job of catching humans? How much negative pressure do those things generate? Standard atmospheric pressure is something like 1.7 elephants sitting on you - we don't notice because it cancels out in all directions - so if the engine is sucking half that away behind you, you have 0.85 elephants sitting on you not canceled out, and you probably still get squished.


text:
Who do you talk to in Class G airspace (UK)?
I'm currently in my early days of learning about aviation, and have just started learning how to use a VFR chart. One thing that I have noticed is that the class D airspaces generally have frequencies to contact the controller for that airspace. Outside of CAS however, there is nothing. Do you just tune the FIS frequency? I understand that the airspace isn't really controlled, but can you still ask for Traffic Service etc?

You want CAP 774: UK Flight Information Services.  That document lists the air traffic services provided to aircraft in class G in the UK.
The services listed are:
Basic Service:

A Basic Service is an ATS provided for the purpose of giving advice
and information useful for the safe and efficient conduct of flights.
This may include weather information, changes of serviceability of
facilities, conditions at aerodromes, general airspace activity
information, and any other information likely to affect safety. The
avoidance of other traffic is solely the pilot’s responsibility.

Traffic Service:

A Traffic Service is a surveillance based ATS, where in addition to
the provisions of a Basic Service, the controller provides specific
surveillance- derived traffic information to assist the pilot in
avoiding other traffic. Controllers may provide headings and/or levels
for the purposes of positioning and/or sequencing; however, the
controller is not required to achieve deconfliction minima, and the
pilot remains responsible for collision avoidance.

Deconfliction Service:

A Deconfliction Service is a surveillance based ATS where, in addition
to the provisions of a Basic Service, the controller provides specific
surveillance- derived traffic information and issues headings and/or
levels aimed at achieving planned deconfliction minima, or for
positioning and/ or sequencing. However, the avoidance of other
traffic is ultimately the pilot’s responsibility.

Procedural Service:

A Procedural Service is an ATS where, in addition to the provisions of
a Basic Service, the controller provides restrictions, instructions,
and approach clearances, which if complied with, shall achieve
deconfliction minima against other aircraft participating in the
Procedural Service. Neither traffic information nor deconfliction
advice can be passed with respect to unknown traffic

These aren't always available and you don't have to use them.  A Basic Service will let an ATS provider know you are there & I've had warnings about unusual activity (police helos, helimeds or fast jets letting down in class G) but I pretty much expect to be ignored.  Traffic services are great but are often withdrawn at busy times (when you most need them) due to controller overload!
Even if I'm not recieving a service, I'll usually listen in to the local frequencies just for situational awareness.  Also, if you're passing close to an ATZ, it's good practice to let them know where you are and where you're going.

Class G is uncontrolled free airspace. You don’t have to talk to anyone if you don’t want to.
If there is a nearby radar facility then you could call them and ask for a service if you like but it’s not mandatory.
In my opinion the ability to just go flying without talking to anyone or filing anything is one of the advantages of the way UK airspace is organised.

Re "In my opinion the ability to just go flying without talking to anyone or filing anything is one of the advantages of the way UK airspace is organised.".   +1 on that, especially in relation to cloud flying!  Might come in handy, especially in the context of glider flying.


text:
Can a non-US registered aircraft be based in the US?
I am a Swiss citizen and I might have to move to the US for a couple of years. I own a small plane in Switzerland (HB-registered) and I'd like to take it with me to the US. As my stay in the US would be for a relatively short period of time, I'd like to keep it HB-registered. Is it possible to do that knowing that the plane would be based and primarily used in the US for that period of time?

I can't find any kind of maximum duration visit in 14 CFR.  I'd recommend calling the FSDO nearest your intended location.

I would recommend comparing the cost/effort of getting your plane across the Atlantic (twice) compared to renting something once you are in the US

@MaxR thanks for you advices I will definitelly contact them!

@757toga thanks for you advices I will definitelly contact them!

@EugeneStyer Is it easy to rent a plane for a several weeks (to explore the country during holyday) in the US? Because in Switzerland it's a huge pain, nobody will rent you a plane for more than a couple of days. That's why I chose to buy...

@Shadow_Heart The whole "bring vs rent" decision is indeed complicated.  There are some places that do long term rentals, where you lease a plane for 6 months, but they are not common.  I agree that most FBOs focus on training and that makes it very hard to do long-term rentals.  Getting a less-flown SR20 for a week or two may be easier than getting a heavily-flown 172.  Again, try calling several FBOs in your destination area before deciding.  Your usage patterns matter--over the 2 years, how many total hours do you expect?  And how many longer trips beyond 3-4 days do you expect?

@MaxR It's difficult to say how much time I'll have to fly when in the US, but here in Switzerland I usually fly aroud 60-70 hours a year and go for longer trips 2 times a year.

@Shadow_Heart You may find that wherever you are going, there are clubs that would work.  A shareowner club doesn't work well for say, a 6 month stent but two years is long enough to justify it.  A 4-5 plane club might cost 5,000 to 10,000 USD to buy into, but you would get that back when you sell your share down the road.  A lot of clubs are set up in such a way that 5-10 hours per month is easy to schedule, and a week or two trip once a year would work fine.


text:
How did the long loop of tape in a magnetic cockpit voice recorder work?
How was the continuous looping of tape in an old-school mechanical cockpit voice recorder physically implemented? 30 minutes seems like a lot of tape to loop continuously, did it move more slowly than a normal audio tape?

you do understand that the tape is an actual loop because on the tape spool, the inside end of the tape has been pulled out of the spool and spliced together with its outer end?

I think it's clear that the OP didn't know that, which is the reason for the question.  The question is based on the obvious meaning of "loop" in the sense that a belt or a rubber band is a kind of loop.  I think this is a good question.

Most looped tape mechanisms are a variation of this:

(this is an 8-track audio cassette)
The tape is pulled from the center of the spool, and fed back to the outside of the spool.
Some CVRs use two spools and autoreverse instead.
On the right, an example of a flight data recorder. (on the left, the digital storage of a modern FDR).

I thought that most flight recorders used wire instead of tape.

Early ones used wire, but tape was also used (https://airandspace.si.edu/collection-objects/magnetic-tape-cockpit-voice-recorder-cvr-aircraft/nasm_A19950038000)


text:
How is camouflage paint applied?
A comment on this answer suggests that the exact paint distribution of a camouflage paint job varies from individual to individual:

Looking closely at the camo details, the a/c in photo in answer is clearly the exact same individual airplane as the one in question —quiet flyer

Production of camouflage in other settings, such as textiles, produces camouflage patterns that repeat predictably enough that the patterns are trademarked, but quiet flyer's comment suggests aircrait camouflage is more like fingerprints.
How does application of a camouflage paint job to an aircraft differ from the usual predictable and consistent process of applying livery?

"quiet flyer's comment suggests aircrait camouflage is more like fingerprints." – That's not what the comment suggests. The comment suggests that camouflage for Tachikawa Ki-54s built before 1945 is individualized. Which, to be honest, doesn't surprise me, since I am pretty sure that no aircraft paint job in that time would have been done by a computer-controlled robot, but by humans instead, who are fallible and inexact.

May be dependent on situation-- for example wouldn't be surprised if some of the larger-scale patterns used in WW 2 (think of a typical Battle-of-Britain RAF Spitfire) might have at least followed a highly standardized pattern, if showing some slight variation due to freehand application. (I'm not sure how standardized these really were, and haven't tried to do research, hence not posting as real answer.)  But the position of each of those individual little dots on that Japanese a/c -- no way would those have been standardized.

"like fingerprints" means individualized.

It's the same basic process as tartan paint. https://www.youtube.com/watch?v=z1RMVG5Tk6E

Unlike airliners, military aircraft are NOT exact. This has a hand in foiling adversarial pattern recognition.
5th Gen fighter, F-22

This from www.military.com

This from https://theaviationgeekclub.com
You can clearly see the difference on the inner surface of the right vertical stabs.
They are given general guidelines as to percentage. And especially, along seams, one type of paint vs another.
The paint on these is applied by robot, to ensure a totally uniform coating.

The F-22—also a fifth-generation stealth fighter—has a different camouflage, which sources have said plays a role in confusing adversary imaging infrared systems. The application of the darker F-22 camouflage shapes, known within Lockheed Martin as “the amoebas,” is an extremely precise process requiring robots to ensure that the paint has no high or low spots that would affect the aircraft’s radar reflectivity.
https://www.airandspaceforces.com/usaf-new-camouflage-paint-for-f-35-aggressors-doesnt-interfere-with-stealth/

F-16 Aggressors at Nellis AFB

https://automototale.com/wp-content/uploads/2019/06/cautofotoaa1313-840x420.jpg
The two on the left, grey/blue are different from each other, as well as the next two (green/brown)
Again, the paint shop is given general guidelines. These 4th gen jets are painted by hand. Well, spray...
Additionally, 2x C-130 from the 37th Tactical Airlift Sq, Rhein-Main AB Germany, 1981.

Same squadron, same time, slightly different pattern.
https://nara.getarchive.net/media/right-side-view-of-three-c-130e-hercules-aircraft-camouflaged-in-european-paint-933866

Makes sense. Making an aircraft sized template to mask off the primer and the "not green" areas would be... cumbersome.


text:
VOR Ground Station
i KNOW THAT VOR Ground Station is aligned with magnetic North. It emits two signals:
a 360° sweeping variable signal
an omni-directional reference signal
When an aircraft receives those it can know its position and radial.
My question is, is it possible the aircraft receive only the reference signal???
Making the pilot know the direction to the station and not the radial he's on.

As Adam says, the "lighthouse" analogy is a very neat and intuitive analogy, but it is just that. The actual operation of a VOR is not quite as intuitive. Watch the first five minutes of this really good video for more.

To 757toga's point, you CANNOT know the direction to the station and NOT know which radial you are on.  It's like saying that you want to know which way North is, but not know which way South is.  For that reason your question really doesn't make sense.

Further to 757's and MH's point...  Yes, you could build a direction-finding antenna and sense the direction of the VOR from you.  But a DF antenna requires either a phased array or, like ADFs, a motorized dipole loop.  Manufacturers don't do that, because no one would buy it, because it's antithetical to the design purpose of VOR.  It's adding cost and complexity for no benefit.  But no, there is no technical reason at all why it couldn't be done or wouldn't work.  It's just a feature that no one wants, and therefore not viable to build into a certificated product.

"Making the pilot know the direction to the station", we cannot determine the bearing of the reference signal, the VOR receiver antennas are not directional, contrary to an ADF. This is why a second signal is required. See this question or this one.

You have a misunderstanding about the operation of the VOR.  From the phase of the two signals it is possible to determine the radial, but not the location of the receiver (or distance).  In order to get the distance it is necessary to use DME.  DME can be colocated with a VOR so at times they might be (technically incorrectly) used interchangeable.  I suppose it would be possible to construct a directional radio receiver, similar to an NDB receiver, that attempts to find the direction to the VOR.  But, I've never seen a VOR receiver that is able to do this.  Any VOR that I've worked with requires the both signals, and then uses the phase difference between them to determine the radial.

+1 "I suppose it would be possible to construct a directional radio receiver", actually you just need a directional antenna and examine the signal strength for all azimuths.


text:
F1A COMPETITION GLIDER
I am working on a school project. I have looked up the airfoil database. There is a wide range of airfoils I have tried to optimize for my glider to no avail. How do i choose the best airfoil for a F1A competition glider?

Technically, this is for Drones and Model Aircraft.SE, but you are more likely to find answers here. Generally, at this level, just look at what others are doing for this class. Everyone tries to "optimize" their competition models. Now, had you asked about F1B, I would offer some answers off the top of my head...

Go ahead bro. I am designing  a free flight glider. That Idea you have can help me a long way


text:
Does a fighter aircraft slow down when firing machine guns?
I imagine the recoil of a powerful machine gun or cannon would decelerate a plane significantly. Is this an issue?

Short version of the answer: No.

Significantly?  No.  Compare the mass of the ammunition being fired to the mass of the aircraft.  For a .50 caliber, typical bullets weigh about 40-50 g.  Say the gun fires 20 bullets per second, that's about 1 kg per second.  A typical fighter, say an F-16, weighs something over 9000 kg.  Muzzle velocity would be about 900 m/s, vs a subsonic (jet) speed of 200-300 m/s.


text:
Can fuel sloshing in the tanks cause a stall?
Cargo planes secure their load meticulously and if it breaks loose, the result is sometimes catastrophic. However, how do you prevent fuel sloshing inside the tanks and causing the same problems as loose cargo?

The answer is no, but some shifting of the center of gravity (c.g.) due to attitude is unavoidable.
Tanks are subdivided so the c.g. shift within a single tank is small. You can notice the sloshing after a landing when the aircraft has come to a complete stop after taxiing: It will gently rock back and forth due to the sloshing in the tanks.
Some fighter aircraft use a sponge-like mesh in their tanks which is very effective in breaking up sloshing. It takes up approx. 2% of internal volume. However, in a nose-up attitude the fuel will still collect at the back of the tanks, and again only distributing fuel over several tanks will prevent a significant c.g. shift.
Subdividing also helps in spanwise direction to prevent high loads on wing ribs when the aircraft rolls. Remember, an F-16 has a top roll rate of 720°/s, which creates a significant inertial pressure on the wing's tank walls.

Naive question: When you mentioned noticing the sloshing after landing, was that in small airplanes or can you notice even in bigger commercial aircraft?

@curious_cat: The most noticeable case was in a Boeing 737-300 of Türk Hava Yollari (todays Turkish Airlines) in Ankara. I guess the captain wanted to impress the co-pilot (or vice versa, I don't know) and braked super-hard to a full-stop landing. After a few seconds of rest (with the aircraft rocking back and forth from fuel sloshing) he accelerated to the next exit, which was still 100m ahead of him. That is one of the rewards of flying with airlines from countries with a Macho culture.

BTW that sponge-like-mesh is used in the tanks of racing cars.

There are dividers (baffles) in the fuel tank precisely to stop the sloshing. They are just large plates that will stop the fuel from flowing across.
High maneuver jets will use bladder tanks (so no air is in the tank with the fuel) as a way to contain the fuel.

don't the dividers have holes in them near the skin, to allow the fuel to redistribute itself when the plane is straight & level again? if not, why not?

Yes, they have (relatively) small holes.  Flow is not prevented, just slowed down.

It would theoretically be possible for sloshing fuel to shift the center of gravity (CG) enough to cause an uncontrollable pitch up, leading to a stall. Designers know this and use various methods to prevent fuel from shifting too much when maneuvering.
First of all, the fuel is generally stored close to the CG (at least longitudinally, which is in pitch), mostly in the wings and sometimes in the fuselage between the wings. This is to prevent large changes in the CG as fuel is consumed during the flight. So while fuel certainly is heavy, movement will be close to the CG and affect balance less.
As Peter Kämpf notes, roll conditions are important as well, and of course having fuel out in the wings will affect latitudinal stability (but also longitudinal with increasing wing sweep). One way to control this is through the use of baffles (or subdivisions). These limit the amount of area available for the liquid to move between areas, preventing large changes during maneuvers but allowing enough fuel to flow during regular fuel burn, refueling, or tank tranfers. Baffles have the added benefit of providing more structural strength, which is particularly important in aircraft. Wing ribs act as baffles in the wings.


text:
Does an aircraft landing on a carrier increase the carrier weight before it touches down?
The same question goes for any runway, but I guess that for small aircraft carriers, one might actually be able to measure the exact point of weight increases (e.g. measure the submersion of the hull). For helicopters, it seems that this is the case, so I would presmue the same for fixed wing aircraft.

Are you asking how a ~ 22 ton F-22 will affect a 100,000 ton USS Gerald R. Ford?

Seems like a good question for http://physics.stackexchange.com .

We seems to have rather strong disagreement between yeas and noes, and only experts on physics can decide. Or maybe we can agree that effect will be very small and not measurable (but not zero).

I think you're asking whether there's a down-draft (force), onto the landing deck, that's equal to the weight of the plane. My guess is that the answer is "no": that what keeps the plane in the air isn't downdraft or at least isn't only downdraft (unless it's a VTOL jet or a rocket), rather it's a partial vacuum (i.e. a low-pressure system) on the upper surface of the wings.

Unclear. What do you mean by weight? The common definition is W=mg. The mass of the carrier doesn't change, nor does the gravity. Although one could argue the aircraft's gravity field will attract the carrier so the result is the carrier being lighter, everybody will agree that the effect is negligible. It seems you are looking for the effect of the aircraft's pressure field on the carrier's deck, @PeterKampf covered that one. For those arguing that the carrier's weight increases only after the aircraft touches down: why do forces subjected through rubber tyres count, but through air don't?

@Ryno can you show the [meta.aviation.se] or [meta.se] discussion where reasoning validity is a requirement for commenting, pretty please? (If you can, I'll gladly delete this comment, if you cannot, your comment is rude, IMHO.

@DavidRicherby - "IF the plane's vertical speed is decreasing..." - if it isn't decreasing, that doesn't make the reasoning wrong.  And I maintain that it must be decreasing, or the plane will hit the deck with too much vertical speed.  Whether all of the lift force will act on the deck depends on the height of the plane.  I maintain that shortly before contact, it is close enough that all of the lift force IS acting on the deck.  It will be spread over more than the footprint of the plane, sure, but still on the deck.

@Ryno My understanding is that carrier landings are done pretty hard. At any point, some of the lift force is coming from work done against the viscosity of the air. At any point, not all of the lift force of the plane is transmitted through the column of air below it to the "ground" below.

+1 to DeltaLima for mentioning the upwards gravitational force on the boat from the airplane itself. Also, the increased density of air molecules near the deck would create even more upwards gravitational force. :) I tend to disagree that this question is really off-topic here. Sure, it's a physics question, but, definition of weight aside, the primary portion of the answer to that question is an explanation of how wings create lift, which seems decidedly on-topic for Aviation SE. It seems like we should have no shortage of aerodynamics experts at Aviation SE.

@Farhan ... I think an F-22 landing on the Ford would be there for a while ... their gear and landing hook are too weak and will break, and (last I checked) they have no catapult attachments. (Granted, they may have enough thrust to takeoff unaided.)

No. Weight is defined as the effect of gravity on a body. Until the aircraft becomes part of the body of the carrier, it has no effect on the weight of the carrier.
I think you are confusing force with weight. For example, if wind shear drives wind against the top deck, this does not make the carrier have more weight, but it does cause the carrier to move down. Likewise any gust from an aircraft may apply a force to the carrier, but does not increase its weight. You might consider that force to increase the "apparent weight" of the carrier, but it cannot be said to increase the weight of the carrier itself.
Note also that the downward wind force of a landing fighter is relatively slight. For example, a person can easily walk under rotating helicopter blades and still stand up and walk. The force is probably only around 1-2 pounds per square inch, maybe 5,000-15,000 pounds total. For an aircraft it will be even less.

I generally agree, but helicopters don't weigh 72,000.  Hovering, a helicopter should displace it's weight in air.

Not sure how this (IMHO) obviously wrong answer gained 3 upvotes. @Peter Kämpf is right. Maybe we should let physics exchange to decide this one.

@SHAF just because a helicopter weighs a certain amount does not mean that amount of force is applied to the GROUND. The PSI will show a gradient from the blades to the ground. At the blades it will be the weight of the helicopter, but then it will decrease from there.

@PeterMasiar You are right it is a physics question, but just claiming somebody is "obviously wrong" without giving any reason is against the principles of Stack Exchange. Consider that you have 0 reputation and no credentials whatsoever, and have offered no reasoning whatsoever, its kind of BS for you to go around talking about how wrong somebody is.

@SHAF Yes, I recomputed the PSI, appears to be only 1-2 PSI.

@PeterMasiar Peter Kampf is incorrect, the weight of the carrier doesn't increase until the aircraft touches the deck. Displacement increases as a force is applied, but the weight remains the same.

@Tyler Durden Downward force towards carrier before landing is slight but not zero. I might not have aviation credentials but remember my Newton laws. If you disagree, take it to physics experts to decide.

@PeterMasiar: Perhaps you've misunderstood this answer. The air underneath a landing aircraft does push the carrier down, but 'weight' is not the correct name for this downward force; that name is reserved for the component caused by gravity.

OK I can see that it is not "aircraft weight" what changes - but result (downward force on the aircraft) will behave exactly like increased weight (will push carrier down, and so slightly that it will be not measurable). So we need to define "before". :-)

@PeterMasiar Weight is a force. Any other force is a force. In that sense, all forces "feel like weight". But that doesn't make them weight.

@TylerDurden You are mistaken; a helicopter does not "push" itself away from the ground, rather the rotor blades generate lift (they are mini-wings, essentially), "pulling" it upwards into the air. Obv we know that there is an opposite reaction of downward force from the blades, but it does not necessarily represent X proportion of the aircraft's weight.

@Jongosi Actually, it does. It represents 100% of the aircraft's weight (directly underneath the blades, at least... the effect on the ground will be less.) The total force applied to the air under the rotors of a hovering helicopter will be exactly equal to the lift generated by the rotors, though. As with all forces, the forces are equal and opposite.

@reirab No, it does not. The primary force opposing the helicopter's weight is lift, not downward thrust. Google vindicates me; https://www.google.co.uk/search?&output=search&sclient=psy-ab&q=how%20does%20a%20helicopter%20work&oq=&gs_l=&pbx=1&bav=on.2,or.r_cp.r_qf.&bvm=bv.82001339,d.d24&ion=1&biw=1434&bih=855&ech=1&psi=0QusVLW0HMm4Ud-2g6gL.1420561348726.3&ei=1AusVInIIov4UtnygKAL&emsg=NCSR&noj=1 A helicopter pulls itself into the air, it does not push away from the earth.

@Jongosi Downward thrust is lift, at least for all practical purposes. You could argue that part (or most) of the lift is generated by 'pulling' air downward rather than 'pushing' it downward, but, either way, the downward force excerpted on the air is exactly equal in magnitude to the weight of the helicopter when it's not accelerating vertically. When moving horizontally, the airframe itself probably also generates some lift, but, again, it's generated by deflecting air downwards. Regardless of whether it's pushed or pulled, the change in momentum of the air will equal that of the aircraft

This really has nothing to do with the question, but for the record most of the vertical force of a helicopter blade is due to positive displacement of air dependent on the the blade pitch angle not airfoil lift. In fact, it is possible to make a propeller or helicopter rotor out of a completely flat blade that is not an airfoil at all.

Excellent question! Yes indeed, it does! At least in the sense that it is pushing the carrier down. Now we have an intense discussion going on if this is weight or not. If we avoid the nitpickers and call it a downforce, I think all will agree that the landing aircraft adds a downforce equivalent to its weight to the weight of the carrier, once it is flying above the deck. Before, this downforce was acting on the water surface (and on the ocean floor ...).
Lift is created by pushing air down continuously, and this air movement has to be stopped somehow. In the end, this stopping happens by friction as long as the aircraft is at altitude. The movement is dissipated by shear forces between the air molecules. Close to the ground the movement is not stopped by shear force, but by a pressure field. Below the aircraft is an area of higher pressure, and this pressure pushes the aircraft carrier down.
Even the high-flying aircraft creates an area of slightly higher pressure below it, but the area is so big that the pressure increase is extremely small. In the end, the mass of the whole earth does not change when an aircraft takes off or lands somewhere.

Lift is primarily created by a pressure differential above and below the wing.

@kjmccarx: Yes, but how is this pressure difference created? And what happens to the air once it has left the wing's surface?

@kjmccarx: Don't forget about the law of action and reaction. If the air applies upward force to the wing, the wing must reciprocally apply downward force on the air.

Yes I would say there's no net increase of pressure on the ship itself. This would be a fun experiment to do with RC aircraft though.

Newton or Bernoulli?

A Mythbusters episode was devoted to this, in this case to a truck full of flying pigeons. I suppose Youtube could be your friend.

I think you are confusing displacement and weight.

You are right that the approaching plane exerts a downward force on the carrier. But that force is not weight. Weight is the force of gravity on a mass, not the force of air displaced by a plane on that mass.

@DavidRicherby: It depends on how you define weight. The mass of the carrier does not increase, but now it has something on its deck that was not there before and makes it sink into the water. If that is not weight, what is it? Pressure, yes, but that is only the means how this force acts on the carrier. What would you call the force, if not weight? Aren't you confusing mass and weight?

The weight of an object is the force of gravity on the object and may be defined as the mass times the acceleration of gravity http://hyperphysics.phy-astr.gsu.edu/hbase/mass.html http://en.wikipedia.org/wiki/Weight#Gravitational_definition  any other force is not weight, but an external force. It's not nitpicking, it's the official definition of Weight.

@PeterKämpf If you want to say that the weight of the carrier has increased after the plane has landed, because the plane now counts as part of the carrier, that's fine. Before the plane has landed, it does exert a downward force on the runway but that force is not the weight of the plane and it does not contribute to the weight of the carrier. It is just a downward force. And no, I'm not confusing mass (amount of matter) with weight (the force exerted on that mass by gravity).

Actually, yes it does make it weight more, while the plane is still in the air, but over the carrier:
While the force the plane actually exerts downwards on the carrier does not directly increase the carrier's weight, that same force does lower the carrier (minutely) in the water as it displaces slightly more water.
Therefore, since the carrier is now less far from the center of the planet, the force excerpted by gravity on the mass of the carrier is now (minutely) stronger, so the carrier weighs more.

Ha! Nice piece of lateral thinking.

But how does this effect compare to the gravitational force that the plane itself (and the increased density of air under its wings) applies to the carrier? My guess would be that the plane and air's gravity would win because gravity follows an inverse square law. The arm from the CG of the carrier to the CG of the air and aircraft is decreasing by orders of magnitude while the arm from the CG of Earth to the CG of the carrier is decreasing by an extremely small amount. Of course, both forces are negligible, but +1 for pointing this out anyway. :)

As other answers explain, it's not the weight that increases, because the mass does not increase.
But there is a downward force that adds to the downward force of weight.
It is caused by the ground effect, which leads to an increased pressure under the aircraft, if it is flying lower than roughly its wingspan.
The added downward force is the force caused by the increased pressure over the area of carier surface.

Everything depends on what you meant by "weight" in

aircraft landing on a carrier increase the carrier weight

Don't confound

mass
gravity force applied on a mass by the Earth
and the collection of forces components pointing down to the center of earth including ground effect pressure (or induced air pressure produced by a fluid that has been moved by another object)

By the way, applying a downward pressure aft of a long floating thing will produce a momentum that induces lift on the front part of that thing (center of buoyancy) due to the principle of flotation which involves displaced water equivalent to the total mass of the thing.
Then comes a consideration about thing, ie, what system are you talking about ?
The aircraft carrier is an object floating on the water while the aircraft is a moving object that exerts forces on anything in its vicinity including air, ground, whatever... until this aircraft landed, taxied out, applied parking brakes (and tied to the flight deck) At that moment, the aircraft can be assumed as non moving part of the boat and the system mass becomes boat mass + aircraft mass => defined new (and non moving) center of gravity with a new weight.
So ?
Weight is the force applied on an object due to gravity. Assuming changes in mass, of the aircraft carrier as well as the aircraft can be neglected, and the two objects are close enough to have the same local gravitational magnitude, we can safely declare their weight doesn't change whatever the aircraft is doing. The weight of the system [aircraft carrier + aircraft] is also constant.
So what is changing.
Everything but weight !

Pressure (fluids)
Contact forces (impact, or much more complex at molecules level with moving air)
Friction (induces momentum)
Stress (at a neglectable scale, but exists anyway)

All this actually induce movement of the aircraft carrier due to the landing plane before, during and after its landing. Whether that movement is neglectable or not only depends on your taste, but it does occur whatever you may think.
In computing, just like trying to simulate a stellar system, even multithreading can't cope with continuously (analogic) varying forces simultaneously applied. But human brain can imagine it.
Everything becomes ultimately complex when you think of permanent oscillations, vibrations turbulences or viscosity. The models we are currently using doesn't allow you to get an exact answer allowing to know the precise vector defining the forces applied by a landing plane on a carrier. You can separate the logic in many small parts, but you'll always have to neglect one or several criterias to get as close as possible to what is really happening.
Measure the submersion ?
Ocean is not still water. And air is compressible (high pressure/low pressure) Due to everything I said above, unless you know every parameter at any given time, you can't measure submersion... and at that scale...
Try this :
Take a (precise and working) roberval balance, and a paper (A4). Hold the paper horizontally above one of the plates, like 6 or 8 inches above. Drop the paper. You'll notice the arrow telling the weight will move towards the plate on which the paper is landing, but will come back nearer to the center. Neither the weight of the paper or the balance has changed, but new forces came into action when you dropped the paper : Air pressure, contact forces, friction...
Want another example ?
Imagine a very wide window on your roof (to get a panoramic view of the sky at night) Then take an F14 or an F22 and make it fly supersonic some feets above your house... Weight ? No. Air pressure.

Insomuch as the aircraft is flying in ground effect, yes, it exerts a downward force on a runway or aircraft carrier before the wheels actually touch down.  This is not weight, per se, but it has the same effect on the runway/carrier.  This is true for fixed-wing aircraft and helicopters.
Helicopters are better known for having significant ground effect.  Indeed, if you see a helicopter flying or hovering over water, and the surface of the water is visibly disturbed by the rotor-wash (downward moving air from the rotor), the helicopter is flying in ground effect.  In which case, it's pretty easy to visualize.  One of the more difficult tasks in flying a helicopter over uneven terrain is the fact that you may be going in and out of ground effect as you cross the terrain.  This makes, at best, for a bumpy ride.  At worst, crossing a narrow chasm can cause you to go out of ground effect, drop significantly, and collide with the opposite side of the chasm.
Do a YouTube search for "ekranoplan" (Russian term) or "Caspian Sea Monster" (western term for the same thing).  This was a very large wing-in-ground effect vehicle the Soviets were developing during the Cold War.  The aircraft was amphibious, meaning it took off and landed on water.  Even when the aircraft is "flying," off the surface of the water, the water underneath is visibly disturbed by it.

The term "amphibious" does not mean the ability to take off and land on water.  Amphibious means it can operate on BOTH land and water. And "Caspian Sea Monster" is a  nickname for the ground-effect vehicle you describe. Sometimes these vehicles are described as WIG vehicles - Wing in Ground Effect.

The weight of the carrier + airplane system begins to increase when the wheels touch and gradually reaches a maximum when the wings stop providing significant lift. It should be obvious that when the plane is in the air, it has no effect on the weight of the carrier, and equally obvious that when the plane is at rest, the weight of the carrier + plane system is exactly the full weight of both vessels added together.
The airplane only puts a momentary twist into this action. The apparent weight of an airplane at touchdown is very small, and increases as the plane settles. This is also obvious if you watch the gear suspension depress during the roll out.
You can do an easy experiment to verify this. Slowly lower a weight onto a scale. The measured weight will increase gradually as the 'lift' provided by your hand decreases to zero. Lateral motion and air pressure and the fact that an airplane is "self-lifting" can really be ignored here.

This answer is just plain(plane?) wrong.  It's factually incorrect.  The fact that an airplane is "self-lifting" cannot be ignored.  When you pickup a weight, that extra weight is supported by your body, and that weight is exerted on the floor through your feet.  Whatever is "lifting" a weight, the weight is exerted downwards somewhere... in this case, on the deck of the boat.  The answer above is correct...

Don't freak out dude, that's exactly what I said. The weight is on the deck of the boat. When the plane is in the air, it's not. The airplane pushes a small amount of air down to the deck and this may produce a force against the boat, but it does not increase the weight of the boat, and as mentioned above, the net force over the area is zero anyway. So, ignored.

No. The weight of a system is the force caused by gravity acting on its weight. The weight of a system is independent of whatever other forces might be acting on it. Scales only measure weight when they are in equilibrium, i.e., when the scale is the only thing supporting the object on it and nothing is moving. While you slowly lower an object onto a scale, the scales are not in equilibrium so the number they display is not the weight of anything.

That's what you said, and you were wrong.  With the assumption (that most people have made) that by "weight" we mean "downward force on" - there IS an increase in downward force on the deck before it touches down.  The plane pushes down on the air, and the air pushes down on the deck.  Before the plane is on the deck, it's weight is being exerted downwards on the deck indirectly.  That's what's incorrect about your answer.

If we are strictly talking about weight (the effect of gravity on mass) then the boat's weight never changes.  Ever.  No matter what you do, or put on top of it.

And I'm saying absolutely not. The airplane wing produces a local pressure gradient whose net force is zero.

@Jasmine : "The weight of the carrier + airplane system begins to increase ..." That's the incorrect part discussed here ;) The force applied by the system Boat+Aircraft on the water below is what you call "apparent weight" but is not weight. It's combined forces not all pointing down (AC lift is also produced by low pressure air above the wings - ground effect is a building up pressure) When decelerating, gears produces pressure due to momentum caused by tail hook braking. Anyway, a 4G impact isn't weight either. It's a contact force => series of landing load and recoils...

@Jasmine. But what you said makes sense (in a way) and is much more "understandable" than a plain physical explanation. That's why I think it doesn't deserve a downvote nor extensive arguing (but it's just me) Just like Peter Kämpf said, it depends on what OP assumed to be weight...

@Jasmine I understand that that is what you are saying.  It is incorrect.  You don't need to keep repeating yourself, this is not a misunderstanding of your answer.  The "net force over the area" is NOT zero!

Again, no. The ground effect does not create a force against the ground. That isn't even how it works in the first place. Ground effect is about disruption of the wing vortex, not about "air pushing on the ground" which would have no effect on the aircraft. http://en.wikipedia.org/wiki/Ground_effect_%28aerodynamics%29

@Jasmine From paragraph 2 of the "Principle of Ground Effect" section of the wiki you linked: Flying close to a surface increases air pressure on the lower wing surface, known as the "ram" or "cushion" effect, and thereby improves the aircraft lift-to-drag ratio. The increased air pressure acts against both the lower wing surface and the ground surface. Ryno is correct that the net force acting on the ground is definitely not zero. Also, ground effect aside, part of the downwash from the wing acts on the ground.

The part about the weight gradually increasing isn't really true. The weight of the boat remains (mostly) constant (see above answers regarding minute differences due to gravitational forces between the boat the aircraft and slight decrease in distance from CG of Earth.) The weight of the aircraft remains constant (again, ignoring the aforementioned effects.)

The apparent weight of the carrier (i.e. its displacement) will first start increasing when the downwash acts on the deck, then will increase sharply when the wheels hit the deck (because the entire vertical speed of the aircraft has to be stopped over the distance of the maximum of the sum of tire compression + gear strut compression.) Once the vertical speed of the aircraft is stopped, downward force on the deck will sharply decrease briefly, then begin to increase again as the lift from the wings decreases.


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Why are there no longer any biplanes?
Is there an aerodynamic reason why the concept of biplane or triplane has been completely abandoned? Practically all planes were biplanes in WW1, and in WW2 practically none were developed.

Whilst not strictly a duplicate the top answer to this question covers it pretty well.  Essentially in the early years of flight the advantages of biplanes outweighed the disadvantages; as material science and engine power improved this reversed and monoplanes became dominant.

Viking Dragonfly, Pitts Special, Rutan had at least one with canard large enough to count as a wing.

You'd think a bi-plane design would be really good for drones, and should be lighter in weight since you don't need as much structural support as really long wings need. And I'd think the drag problem could be overcome by how you choose to position the 2 wings. MIT and the Japanese have looked at a 1935 design that would use 2 wings to cancel out a sonic boom for supersonic passenger planes.

Firstly, there are:
For example this company currently makes a biplane
But the main reason is that they're inefficient, and don't really do much that a monoplane can't.
They produce a lot of drag compared to the amount of lift they produce, meaning they use a lot of fuel to travel the same distance. They have fairly poor visibility, which is usually considered a bad thing!
They do have a few advantages - they have a good roll rate, making them quite maneuverable, and they have a very low stall speed and can fly on little power, meaning they can fly slowly very well (where their increased drag doesn't make much difference: drag increases with the square of airspeed)
Overall, though, the above makes them suited only to aerobatics, which can also be performed by monoplanes. Advances in wing design and composite materials take away most of the advantages of a biplane for any other use: ie actually travelling (the main purpose of an aeroplane) and carrying a load.
Overall, then, they're more complex than a monoplane, less efficient, and aren't much more manoeuverable. They have more disadvantages than advantages.
Biplanes were popular in WWI not because of any inherent advantage, but simply because technology hadn't advanced far enough to allow any other options. Once the monoplane was properly developed, it allowed much higher speeds (450mph for a late WWII fighter, 300mph for an Early WWII fighter, compared to around 120 mph for a late WWI fighter). High speed fighters beat low speed fighters (at least before stealth technology and guided missiles)
There were a few leftover biplanes in WWII - The Fairey Swordfish torpedo bomber was one of the most widely used, as the low speed and good lift from the biplane design allowed it to carry a heavy torpedo, while the drag issues didn't matter at the slow speeds they needed to fly to be able to release the torpedo properly and on target. Others were the Gloster Gladiator (UK), Fiat CR.42 (Italy) and Polikarpov I-15 (Soviet Union) which achieved varying levels of success in the early stages, but were well and truly outclassed when facing even early-war monoplanes.
This answer on a similar question gives some useful context about the direct advantages and disadvantages. It doesn't directly explain why biplanes fell out of favour, but it may help understand my own answer here.

'they have a good roll rate', could you explain this? It seems to me that the roll rate is mainly dependent on the size and efficiency of the ailerons. Also, more mass far away from the center of gravity would mean a larger moment of inertia.

@ROIMaison - they (biplanes) have LESS mass far away from the centre of gravity because the wings are shorter (up to half the length of a comparable monoplane wing) and can also be lighter in some cases. It also affects how much wing is "resisting" the roll through the air, similar to how clipped wings work - see the Spitfire L.F (clipped wings for roll rate at low altitude) vs the Spitfire F (Regular) variants. Ailerons make some difference, but for a comparable aileron size and wing area, a biplane will roll better than a monoplane

Oh right, didn't thought about the shorter wings :) thanks for the explanation

@JonStory I will suggest to include in your answer that biplane wings produce more drag as longer wings (biggest aspect ratio) produce less drag. On top all the strings connecting both wings produce not needed drag.

Being able to fly at a slow speed seems very important when your civilization is struggling to create light, efficient engines. You know, like the early 20th century.

Don't forget the Antonov An-2 utility biplane, still flying! It is an old design (1947) but is still in production. It's even being constantly updated with new variants being developed as recently as 2013.

Another advantage of biplanes is that they are very good in a bush plane role, where the slow take-off and landing speeds and the short wings help operation in the wilderness where the terrain is rugged and full of obstacles. This is a niche role where biplanes are often used even today. The famous An-2 can land almost anywhere, as it has a stall speed so low it can basically land like a parachute, an impressive feat for an aircraft of that size.

If the purpose of an airplane was to fly around an area at moderate altitude for as long as possible on a given amount of fuel, without having to go anywhere (e.g. for purposes of extended reconnaissance, communications forwarding, etc.) would a monoplane be able to do the job with less energy per hour?  How would its energy requirements compare with those of a non-tethered blimp that need to be able to keep its general position in the presence of moderate winds?

@supercat That's an interesting question, you might wanna post it. I'm pretty sure, however, that the monoplane will be more efficient, but only if it has an engine for travelling at the same speed as the bi-plane. Otherwise, with the drag increasing as the square of the velocity, the extra drag probably overcomes the lesser form drag of the wing configuration. Don't know much about blimps, but if wind speeds are on the order of 20 or 30 kmh, compare that to a biplane cruising at 200 kmh and you can see that overcoming drag (or wind, relative) should be easier for the blimp.

@supercat: Don't forget crop dusters, which also have to "fly around an area at moderate altitude for as long as possible on a given amount of fuel, without having to go anywhere".  Okay, not strictly as long as possible, but if you're spraying a lot of field...

@Sean: I'm not sure if new biplanes are still being manufactured for the purposes of crop dusting, but that was certainly one of the purposes I'd been thinking of, though I forgot to list it except as the "etc.".

Well there ARE still biplanes produced today, either for nostalgic, or recreational reasons; they're just cool and harken back to classic age in aviation.  Biplanes are still popular with aerobatic pilots today for their agility as well.
The chief reasons the biplane largely went the way of the dinosaur have to do primarily with aerodynamics and structural mechanics.  When the cantilevered wing was perfected as well as construction from lightweight, high strength aluminum alloys which facilitated the monoplane, aircraft designers could take advantage of the superior characteristics of a monoplane, specifically much lower drag, allowing for higher speed flight.  World War II accelerated this transition, as the need for higher performance military fighters made the monoplane extremely attractive to designers on both sides.
But a Stearman or a Pitts are still a hell of a lot of fun to fly.


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Do landing planes brake with wheel-brakes or air-brakes or both?
I suppose they do both, but what percentage of the kinetic energy is absorbed by the wheel brakes and what percentage by air-friction (in typical cases)?

Not a duplicate (probably) as the link specifically addresses large jets, and this question is asking about planes, which in the absence of any qualification includes everything from ultralights on up.

Also see spoilers which are used both to increase descent rate at constant speed in flight, and to remove residual lift and increase drag on the ground.

@mins: Yes, especially in sailplanes.  Or in light aircraft, if you're landing on grass or dirt, you might not want to use much braking (skidding, nosewheel digging in, etc), while on a short paved field you'd want full flaps & brakes...

Depends on how long the runway is.
If you have a 12,000' runway and your terminal is at the far end of it, you can roll out with no wheel braking and as little (or no) reverse thrust as you're allowed, and you'll be close to taxi speed by the time you're ready to turn off.  In that case, the brakes only absorb enough energy to get you from maybe 60-80 knots down to 20-30, since the drag devices lose most of their effectiveness by that point.
On the other hand, on a really short runway, you may be getting on the brakes immediately after touchdown, which means that the amount of time that you're dissipating energy due to drag (spoilers) and reverse thrust is reduced, and much less energy is lost that way.  So in that case the brakes get a great deal of your kinetic energy.
The case beyond that would be if you didn't use reverse thrust, your brakes would get nearly all of your energy, with only a small amount dissipated due to aerodynamic drag.